The present invention relates generally to apparatuses and methods for cleaning thin discs, such as semiconductor wafers, compact discs, glass substrates and the like. More specifically, the present invention relates to cleaning hydrophobic wafers using a surfactant containing solution.
As semiconductor device geometries continue to decrease, the importance of ultra clean processing increases. Conventional wafer cleaning and drying methods include one or more rinsing steps either with pure deionized water or with a cleaning solution. Before cleaning, the surfaces of silicon wafers typically are converted from hydrophobic to hydrophilic because hydrophilic surfaces do not attract particles and hydrophilic surfaces help rinsing water and cleaning solution to wet the wafer""s surfaces.
Conversion from a hydrophobic state to a hydrophilic state occurs for example when the surfaces of silicon wafers react with oxygen or an oxidizer to form a thin oxide layer, which passivates the surfaces of the silicon wafer (i.e., forms a passivation layer). The passivation layer is hydrophilic, and thus facilitates subsequent cleaning processes. The surfaces of low-k dielectric wafers (wafers that have a low-k dielectric formed thereon), however, do not react with oxygen or an oxidizer to form a hydrophilic passivation layer. Thus, absent treatment, low-k dielectric wafers have hydrophobic surfaces. Therefore, when aqueous cleaning solutions are applied to the surfaces of a low-k dielectric wafer, the aqueous cleaning solutions are repelled therefrom.
Hydrophobic wafers are more difficult to clean than hydrophilic silicon wafers, due to the poor wettability of aqueous cleaning solutions on hydrophobic low-k dielectric wafers. Also, the efficiency of chemical residues removal by deionized water rinsing is very low. Drying of hydrophobic wafers is even more challenging than cleaning, due to the high affinity of particle contaminants to the hydrophobic surfaces. Further, because pure DI water is typically sprayed directly onto the hydrophobic surfaces during rinsing, water marks or residues are commonly observed on the hydrophobic surfaces during drying. Such water marks and residue may cause subsequent device failure. The semiconductor industry is increasing the use of low-k dielectric wafers and, hence, much attention has been directed to improved methods for cleaning a hydrophobic wafer.
Accordingly, a need exists for an improved method and apparatus for cleaning hydrophobic wafers.
The present invention provides a method and an apparatus that uses a surfactant to clean a hydrophobic wafer. The inventive cleaning method comprises two main aspects. In the first aspect, the inventive cleaning method may clean a wafer by applying a surfactant without using pure DI water. In the second aspect, the inventive cleaning method may clean a wafer by applying a surfactant followed by applying pure DI water during a short rinsing step that is sufficiently short so that rinsing ceases in one aspect, before the surfactant has been completely rinsed from the wafer, thus eliminating or minimizing the contact of pure DI water with the wafer. These aspects may be performed in any conventional cleaning and drying apparatus that is appropriately programmed to perform the inventive method. For example, the inventive methods may be employed within an SRD, scrubber, or within any tank or other type system that includes spray nozzles, any of which may further include application of vapors to achieve Marangoni drying. In a third aspect of the invention, either of the methods described above is performed as a final step in a cleaning sequence that employs a plurality of cleaning apparatuses, and that further maintains a surfactant layer on the wafer during transfer between the plurality of cleaning apparatuses, and that does not contact the wafer with pure DI water prior to the final clean/dry step, if at all.
Other features and aspects of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings.